This invention relates to improved heat exchangers and systems that employ the improved heat exchangers. This invention also relates to methods of using the improved heat exchangers.
Combustion turbines generally include a compressor, a combustor and a turbine section. The compressor compresses air, and the air is directed to the combustor. In the combustor, the air is mixed with fuel, and this mixture is burned to produce a hot gas. The hot gas is sent through the turbine section where a portion of the energy in the hot gas is converted into useful work. This work may include rotation of a shaft which drives a load, such as an electrical generator. After traveling through the turbine section, the hot gas is exhausted from the combustion turbine.
Combustion turbines generally have cooling systems. These cooling systems may be used to cool various components of the combustion turbine, such as the combustor and the vanes disposed in the turbine section. Although various cooling mediums may be used, typically either steam or air is used as the cooling medium. These cooling systems may be closed loop type cooling systems or opened loop type cooling systems. In closed loop type cooling systems, the cooling medium is continuously circulated through the components to be cooled. In contrast, in open loop type cooling systems the coolant is circulated through the component to be cooled a single time.
Generally, combustion turbines may be operated in either the simple cycle mode of operation or the combined cycle mode of operation. In the simple cycle mode of operation, most of the hot gas exhausted from the turbine section of the combustion turbine is exhausted to the atmosphere. However, a portion of the hot gas exhausted from the combustion turbine is directed to a once through steam generator where its heat is transferred to a cooling medium, which may be water or steam. This heated cooling medium can be used by the combustion turbine cooling systems to cool components of the combustion turbine.
Conversely, in the combined cycle mode of operation the hot gas exhausted from the combustion turbine is sent to a heat recovery steam generator. In this heat recovery heat exchanger, heat is transferred from the hot gas to a cooling medium. The heated cooling medium may then be used to drive a steam turbine and in the combustion turbine cooling systems to cool components of the combustion turbine.
In these prior art combustion turbines, a separate heat exchanger was used to extract heat from the hot gas exhausted from the turbine section of the combustion turbine depending on whether the combustion turbine is operated in either a simple or a combined cycle mode of operation. This invention relates to heat exchangers that can be used when the combustion turbine is operated in either the simple cycle mode or the combined cycle mode of operation. This invention also relates to combustion turbine systems and methods of operating combustion turbines with heat exchangers of this invention.